The invention relates to electrical circuit devices, and particularly to a method and means for electrically connecting terminal leads, which extend outwardly from one surface of an insulating substrate, to electrical circuitry deposited on an adjoining surface of the substrate.
Over the past few years, there has been increased activity in providing electrical circuit components as printed or otherwise deposited configurations disposed on one or more surfaces of an insulating substrate member. The material of the substrate member is usually steatite, alumina or other ceramic based composition. Although the deposition of the materials required for supporting the electrical circuitry is usually quite sufficient with regard to the particular adjoining surfaces involved, very often it is difficult to insure that there will be an adequate thickness of the deposition of conducting edge termination material at the intersecting edge of the two adjacent surfaces. The conducting edge termination material is arranged to complete the circuit between termination leads extending outwardly from one edge and the adjacent intersecting surface which is intended to support the thick or thin film circuitry deposited thereon. The edge termination material underlies the deposited circuit layer(s) and under a solder layer on an adjoining surface in supporting contact with terminal leads projecting outwardly from that surface. The circuitry may be relatively simple, as for instance, a resistor network, capacitor electrodes or may include relatively complex semiconductor portions in the form of attached chips or other devices which comprise a hybrid assembly.
Devices, such as those to be hereinafter described, are made in relatively large quantities and are preferably arranged for automated manufacture. That is, the leads are very often attached by using conventional lead frame preforms, or other support carriers for a multiplicity of leads, and are further anchored to the substrate by means of solder applied with well-known solder flow bath or similar facilities. Thus, the leads may be initially held in place by wedging into a substrate opening and transported through a solder flow bath, where the solder will cling to the inner ends of the leads and to deposited solder-accepting edge termination areas applied to a surface of the substrate. The solder does not adhere to other portions of the substrate or the circuit. Techniques of this nature are disclosed in the electrical circuit devices illustrated and claimed in the Bartley et al U.S. Pat. Nos. 4,127,934; 4,187,529 and 4,213,113, and the Beckman et al U.S. Pat. No. 3,873,890, all patents being assigned to the same assignee as the present invention. The first mentioned patent relates to a single in-line packaging technique, (SIP), whereas the Beckman et al patent is directed to a dual in-line package (DIP).
Inasmuch as the edge termination composition is conventionally made from a material, such as silver, which tends to go into solution with a later-deposited solder layer, there is always present the possibility of leaching away of termination material which has been deposited on the adjoining surfaces during soldering operations. This deposition is usually applied by a transfer roller and often is thinnest at the relatively sharp edge defining the intersection of the two angularly relative surfaces. The Applicants are aware of some manufacturers who even go so far as to hand paint this sharp edge to insure a greater thickness of termination material. Obviously, this is a very expensive operation.
The applicants in researching this problem conceived of the present invention, which resides principally in providing an indentation extending between the adjoining surfaces and traversing the aforementioned relatively sharp line of intersection. This indentation may take the form of a simple notch at the line of intersection, or is preferably provided by means of a groove extending across the edge or surface which supports the terminal leads of conventional parallelepiped-formed dual in-line or single in-line packaged components. The groove finds its preference in the fact that molding dies used to press the ceramic substrate to form are easier to machine with a groove, as opposed to being machined to provide a plurality of relatively small protrusions arranged to form notched areas in the substrate. These projections used for notching are also relatively small and subject to early abrasive wear during use of the dies.